1. Technical Field
The present disclosure relates to image sensors, including CMOS sensors with a multiple integration period, called high-dynamics sensors, and to methods of controlling pixels of such sensors.
2. Description of the Related Art
A CMOS image sensor pixel essentially comprises a photodiode used in reverse mode, having its junction capacitance discharged by a photocurrent according to a received light intensity. The measurement of the illumination level received by a pixel is performed by measurement of the voltage across the photodiode at selected times, among which the end of a so-called image acquisition or integration period, before and after which the pixel is reset by recharging of its photodiode. The decrease of the voltage across the photodiode during the integration is proportional to the received light intensity. For high light intensities, the photocurrent may be such that the discharge of the junction capacitance during the integration phase adversely affects the measurement. In particular, beyond a given light intensity threshold, which depends on the integration time and on the features of the pixel elements, the photodiode reaches, before the end of the integration time, a so-called saturation discharge level, and brightness differences are no longer discriminated.
To improve the discrimination between the different brightness levels, control methods with a multiple integration period, that is, comprising several read steps at different times of a same integration phase, have been provided. Such methods enable to extend the dynamic range of the sensor, but however have the disadvantage of introducing unwanted noise into the images.